https://github.com/SiliconLabs/matter_applications/tree/master/matter_thread_sparkfun_weather_station_mad
This project showcases how to add custom clusters to a Matter project, and how to modify Home Assistant to be able to read these custom clusters.
The project does this by utilizing a Sparkfun Weather Meter Kit, which measures Wind Speed, Direction and Rainfall Measurement, for which there are no clusters and attributes yet.
GitHub
Matter wireless applications. Go to https://github.com/SiliconLabs/application_examples - SiliconLabs/matter_applications